But those who back the bill say in reality it will only be used in a small number of cases.

"This is not about lethal injections for children, this is about terminally ill children, whose death is imminent and who suffer greatly," said Carina Van Cauter, from the Flemish Liberal Democrats who back the law.

"There are clear checks and balances in the law to prevent abuse," she said of the legislation, which now has to pass the largely symbolic stage of being signed by the country's monarch.

Children seeking to end their lives must be "capable of discernment", the law says, and psychologists must test them to confirm they understand what they are doing. Parents must also approve of their child's decision.

Those who oppose the law say it is a slippery slope, which could see terminally ill children pressured into deciding to end their lives.

Carine Brochier from the European Institute of Bioethics think tank does not believe the law would apply to only a small number of cases.

"You don't make a law for three people a year, that's really crazy," she said.

"People are getting used to this idea of euthanasia in order to say okay, well if I don't want to live anymore then I will ask for euthanasia. If I suffer the answer is euthanasia."

When asked if she was concerned that more children would make use of the law, Ms Brochier said that supply creates demand.

"If you offer euthanasia then some parents might be tempted to act and to ask for euthanasia," she said.

"Also doctors, would they try to perform more and more in order to alleviate more and more the pain if they know if they are asked they can kill a child."

Brussels Archbishop Andre-Joseph Leonard, head of the Catholic Church in Belgium, asked at a prayer vigil last week why the state wanted to give minors such responsibility when they had to wait until 18 for many other legal rights.

"The law says adolescents cannot make important decisions on economic or emotional issues, but suddenly they've become able to decide that someone should make them die," he said.

The new law specifies that children seeking euthanasia must be terminally ill rather than just in a state of unbearable suffering, which is the qualification for adults.

Apart from Belgium and the Netherlands, euthanasia is also legal in neighbouring Luxembourg, and France is considering legalising it later this year.